1. Field of the Invention
The present invention relates generally to a valve timing control system for an automotive internal combustion engine. More specifically, the invention relates to a valve timing control system which can adjust phase relationship between a crankshaft and a camshaft for adjusting valve opening and closing timing intake and exhaust valves of the internal combustion engine.
2. Description of the Background Art
One typical construction of the conventionally known valve timing control system has been illustrated in the U.S. Pat. No. 4,535,731 assigned to the common assignee to the present invention. In the disclosed construction, a camshaft carries a camshaft synchronous rotary member. On the other hand, a timing sprocket is mechanically connected to a crankshaft via a timing chain for rotation in synchronism with engine revolution. An intermediate gear member of generally cylindrical construction is disposed between the timing sprocket and the camshaft synchronous rotary member. The intermediate gear member has helical gear teeth formed at least one of the inner and outer periphery thereof. The intermediate gear member is axially shiftable by a hydraulic means for causing phase shift between the crankshaft and the camshaft.
In the shown construction, the intermediate gear member is shiftable between a first and initial position and a second shifted position. At the first position of the intermediate gear member, the phase relationship between the camshaft and the crankshaft is maintained at initial phase relationship. When the intermediate gear member is shifted to the shifted position, the phase relationship is vary to advance the valve timing relative to the engine revolution.
Though such prior proposed valve timing control system is successful to improve the engine driving performance in certain aspect, two-way adjustment of the valve timing, i.e. initial timing and advanced timing is not satisfactory in view of the valve timing control precisely corresponding to the engine driving condition.